1. Field of the Invention
This technology relates to wellhead assemblies. More particularly, this technology relates to an arrangement for locking inner well members to outer well members in wellhead assemblies.
2. Brief Description of Related Art
Typically, locking arrangements are used between inner and outer well members to help prevent relative axial movement between the members. For example, known locking mechanisms may lock a casing hanger in a wellbore. One example of such a mechanism is a locking ring, which may reside in a groove in the casing hanger as the casing hanger is inserted into the wellbore. The ring may then expand outwardly into partial engagement with a corresponding groove in the wellhead when the casing hanger is fully seated. While such an arrangement may be effective to prevent axial movement between the casing hanger and the wellhead, multiple parts are required to complete the arrangement, and some mechanical means is required to deploy the ring when the casing hanger is in place. Thus, such a locking arrangement may be too complicated for use in some wells.
Another example of a known locking arrangement is a profile that includes a series of ridges formed on the inner surface of a wellhead. When an inner well member, such as an annulus seal, is inserted into the wellhead it may have pre-cut grooves that correspond to the ridges. Alternatively, the inner well member may be constructed of a material that is softer than the ridges, and energized into plastic deformation around the ridges. The ridges of such profiles typically have a positively angled upper surface and a negatively angled lower surface. One problem with such profiles is that, because the surfaces are angled, any upward force exerted by the inner well member on the ridges has both a vertical component and a radial component. The radial component tends to reduce engagement of the casing hanger from the ridges when under load. In some instances, this may lead to failure of the locking profile and harmful relative axial movement between the wellhead and the casing hanger.